Wednesday, May 30, 2012

Defining the Seasons

As we move between
the solstices and equinoxes it is sometimes asked how we measure the start and
end of the seasons in Australia and why this is different to other parts of the
world.

In Australia we use
the beginning and end of calendar months to describe our seasons – winter is
June 1st to August 31st, spring from September 1st
to November 30th, summer from December 1st to February 28th
(29th in a leap year) and autumn from March 1st to May 31st.

However in other
parts of the world the seasons are defined through the solstices and equinoxes.
In the Southern Hemisphere the summer equinox, or the longest day, falls around
December 21, and the winter solstice, or shortest day, around June 21. (There
is some minor variation of these dates from year to year). The spring or vernal
equinox (equal hours of night and day) falls around September 21st and the
autumnal equinox around March 21st.

If we use these
dates to define our seasons we find that summer occurs between December 21st
and March 21st, autumn from March 22nd to June 21st,
winter from June 22nd to September 21st, and spring from September
22nd to December 20th. This system displaces our present
seasons forward by about three weeks.

So why did Australia
not adopt this solstice – equinox system rather than the calendar month option
that has considerably less physical significance? The answer appears to be lost
in the mists of time but an interesting theory has been advanced that may or
may not be true.

In 1789 the New
South Wales Corps was formed in England as a permanent regiment to oversee the
infant settlement of Sydney. Apparently they changed from summer dress to
winter dress on March 1st of each year and then back to summer dress
on September 1st. This may have been the reason behind defining our
seasons using calendar months.

In any case it’s
also become rather obvious that the four season European model has little
relevance in many parts of Australia. In Darwin, for example there’s a strong
wet season dry season cycle with spring and autumn hard to find.

Indigenous
Australians have a different way of describing the seasons that varies from
place to place and some further details about this can be found at